When I said I let them chew/mouth the toys as long as it's not something "unsafe", this is basically what I meant. If the paint will come off, the foam may rip off, felt may come apart or the glue/marker/paint would be unsafe for mouths in my mind, books coming apart in their mouths etc
If it's safe, easily washable toys hen I have no problem with them mouthing it. (plastic toys mostly which I have a LOT of..)